simplified sc calcs

7/22/2019 Simplified SC Calcs

1/17

Simplif ied Fault Current

Calculations

Presented by:

Dustin [email protected]

Agenda

Basic electrical distribut ioncomponents & relationship w ith faultlevelsTransformers, conductors, etc.

Overcurrent Protective Devices (OCPD)

Simplified fault calculation example

Relevant NEC requirements

Cooper Bussmann Solutions

Fault Current Basics


2/17

X

54,000A Available

X

X

X

X38,000A Available

31,000A Available

35,000A Available

28,000A Available

Available Faul t Current?

TYPICAL SHORT CIRCUIT

CURRENTS

Home Receptacle - 200 to 500 amps

Home Service - 2,000 to 10,000 amps

Bussmann Headquarters - 70,000 amps

New York City - 202,000 amps

St. Louis, MO - 210,000

Chicago, IL - 215,000

Dallas, TX - 220,000

Tulsa, Oklahoma - 260,000 amps

Short Circuit Calculations

Why short-circuit calculations?

Several sections of the NEC relate to proper

overcurrent protection. Safe and reliable

application of overcurrent protective devices

based on these sections mandate that a short

circuit study and a selective coordination be

conducted.


3/17


More on This Later

Sections in the NEC include:

110.9 Interrupting Rating

110.10 Component Protection110.16 Arc-Flash Warning Labels

Art. 240 Overcurrent Protection

409.110 Industrial Control Panels

430.8 Motor Controllers

440.4(B) HVAC Equipment

670.3 Industrial Machinery

Numerous

Articles Selective Coordination


Compliance with these code sections can

be accomplished by conducting a short

circuit study. To obtain reliable operation

and assure that system components are

protected from damage, it is necessary to

first calculate the available fault current at

various critical points in the electrical

system.


Critical points in the system include:

Service Entrance

Panelboards Industrial Control Panels & Machinery

Motor Control Centers

Motor Starters

Transfer Switches

Load Centers


4/17


Once the short circuit levels are

determined, it is possible to specify proper

interrupting rating requirements, selectively

coordinate the system and provide

component protection.

Fault Current Analysis

Simplified method point to point

calculations

More detailed analysis can be done

using commercial software or hand

calculations

Cooper Bussmann short-circui t

calculator

http://www.cooperbussmann.com/7/FreeSoftware.html

MM

MSB

Short Circuit Currents

Vary Depending on Many

Factors

Transformer Size & % Z

Voltage

Conductor Size & Length


5/17

MM

MSB



Factors

60,000 A

27,000 A40,000 A

60,000 A

18,000 A

9,000 A



Factors

How to Calculate Transformer Secondary(assuming infinite primary)

EPR Page 7 KVA SIZE

VOLTAGE

%Z

500 KVA

480/277V

1

5 % Z

500 KVA

480/277V

1A

2 % Z

1500 KVA

480/277V

2

5% Z

1500 KVA

480/277V

2A

2 % Z

Short Circuit Current Examples #1

1500 KVA

208/120V

3

5% Z

1500 KVA

208/120V

3A

2 % Z


6/17

500 KVA

480/277V

1

5 % Z

500 KVA

480/277V

1A

2 % Z

13,377 A

33,444 A

1500 KVA

480/277V

2

5% Z

1500 KVA

480/277V

2A

2 % Z

40,133 A

100,333 A

1500 KVA

208/120V

3

5% Z

1500 KVA

208/120V

3A

2 % Z

92,533 A

231,333 A


How to Calculate Conductor Contribution

EPR Page 7 LENGTH

VOLTAGEC CONSTANT

Isca

208/120V

4

4A

6

6A

480/277V

5

5A

480/277V

40,000 A. 40,000 A.40,000 A.

50 ft # 1 50 ft 250 kcm



7/17

208/120V

4

4A

40,000 A.

50 ft # 1

12,181 A.

480/277V

5

5A

40,000 A.

20,104 A.

6

6A

480/277V

40,000 A.

50 ft 250 kcm

27,820 A.


Simplif ied Fault Calculation:

EXAMPLE

EPR Page 11 & 12, Number (1)

Simplif ied Fault Calculation:EXAMPLE

ANSWER:

SCA = ~42,000 Amps


8/17

Relevant NEC Requirements

NECAdoption

2002 NEC

1999 NEC

Local Adoption2005 NEC 2008 NEC

LATX

CO

OR

WA

MO

NM

IL

PA

CA

NV

AZ

KS

AR

IA

MN

WI

MI

OK

NE

ND

SD

MT

ID

UT

WY

MSAL GA

FL

TN

IN

KY

OH

WV

SC

NC

VA

NY

ME

CT

MA

NJ

NH

VT


Sections in the NEC include:

110.9 Interrupting Rating

110.10 Component Protection

110.16 Arc-Flash Warning Labels

Art. 240 Overcurrent Protection409.110 Industrial Control Panels

430.8 Motor Controllers

440.4(B) HVAC Equipment

670.3 Industrial Machinery

Numerous

Articles Selective Coordination


9/17

IR Exceeded

110.9 Interrupting Rating&

110.10 Component Protection

IR Exceeded

IR Exceeded


10/17

Arc Flash Hazard

110.16 Arc-Flash Warning Labels

Arc Flash Hazard

Fault current effects arc flash hazard level

SCCR

409.110, 430.8, 440.4(B) & 670.3

Equipment Short-Circuit Current Ratings


11/17

What is SCCR?

UL 508A & 2008 NEC

Short-Circuit Current Rating.

The prospective symmetrical

fault current at a nominal

voltage to which an apparatus

or system is able to be

connected without sustaining

damage exceeding defined

acceptance criteria.

What is SCCR?

SCCR is the maximum

current:

a component, assembly or

equipment can safely

withstand

when protected by a

specific overcurrent

protective device, or for a

specified time interval

Simple:

Level of fault current an assembly of components is rated to withstand

X

Motor Controller

Industrial Machinery

HVAC

Industrial Control Panels

54,000A Available

X

X

X

X38,000A Available

31,000A Available

35,000A Available

28,000A Available

What is SCCR?


12/17

What is SCCR?

SCCR markings on equipment labeling

are provided to ensure proper protectionfor assemblies

Equipment SCCR must exceed theavailable short-circuit current at thepoint of installation (NEC 110.10)

Similar to interrupting ratingrequirements found in NEC 110.9

Selective Coordination

517.26, 620.62, 700.27, 701.18, 708.54


NEC 2008 Requirements

Emergency Systems 700.27Illumination, ventilation, fire detection, alarm systems, etc.inplaces of assembly, hotels, theaters, and sports arenas

Legally Required Standby Systems 701.18Safety-related systems such as HVAC, communicationsystems, ventilation, and sewage treatment plants

Critical Operati on Power Systems (COPS)

708.54Public safety-related systems that require continuous operationfor like emergency management facilities or business centers

Essential Systems 517.26Emergency, Critical and Equipment branch in Healthcarefacilities (must meet requirements of Article 700)

New in 2005

New in 2005

New in 2008

Increase Systems Reliability Preventing Blackouts

New in 2005


13/17

What is Selective Coordination

For the full range of possibleovercurrents

LINE SIDE

LOAD SIDE

KRP-C-1200SP

LPS-RK-600SP

Only closest upstream OCPDfrom overcurrent opens

Other upstream (larger)overcurrent protective devicesdo not open


Ar ticle 100 Defin it ion

Ar ticle 700 Emergency Sys tems

Coordination (Selective)

Localization of an overcurrent condition to restrictoutages to the circuit or equipment affected,accomplished by the choice of overcurrent protectivedevices and their ratings or settings.

700.27 Coordination.

Emergency system(s) overcurrent devices shall beselectively coordinated with all supply side overcurrentprotective devices

(Wording for 701.18 and 708.54 is the similar except for the type system)

Without Selective Coordin ation With Selective Coordi nation

OPENS

NOT AFFECTED

UNNECESSARY

POWER LOSS

OPENS

NOT

AFFECTEDFault Fault

System Prospective


14/17

Circuit Br eaker Instantaneous Trip

Up to where the circuit

breakers cross, it is

interpreted to becoordinated. See

800A

200A

30A

Up to

7600A

Up to

1500AX

X

4

4

5

5

6

6

7

7

8

8

9

9

10

10

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

100

100

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

1000

1000

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

10000

10000

2

2

3

3

4

4

5

5

6

6

7

7

.01 .01

.02 .02

.03 .03

.04 .04

.05 .05

.07 .07

.1 .1

.2 .2

.3 .3

.4 .4

.5 .5

.7 .7

1 1

2 2

3 3

4 45 5

7 7

10 10

20 20

30 3040 40

50 50

70 70

100 100

200 200

300 300

400 400500 500

700 700

1000 1000

CURRENT INAMPERESAT 480 VOLTS

CURRENT INAMPERESAT 480 VOLTS

TIMEIN

SECONDS

TIMEIN

SECONDS

1500A 7600A

30A

0.01s

0.1s

800A

IT = 10X

200A

IT = 10X

Reference

IEEE 1015-2006 BLUE BOOK Applying Low-VoltageCircuit Breakers Used in Industrial and CommercialPower Systems

Page 148 5.5.5 Thermal-magnetic MCCBs andinsulated case circuit breakers

It should be noted that if the fault current is above theshort-time rating (instantaneous override), then theICCB will not be selective with downstream devices thatalso have instantaneous trips.

Bussmann Fuse Coordination

No fault levels or plotting required!

LOW-PEAK : LOW-PEAK

2:1 Line:Load RatioLine

Side

Fuse

Load Side Fuse


15/17

Cooper Bussmann Solutions

Quik-Spec Family

Suite of fusible electrical distributionproducts designed to meet Selective

Coordination and other NEC

requirements, providing the numerousbenefits of fused solutions

Cooper Bussmann committed toexpanding our assembly offering,

focused on product differentiation,creating options for fusible solutions

Quik-Spec Family: Coordination Panelboard

Power Module

Safety Switch

One line diagram

With quik spec

products

The New Standard in Fusible Panelboards

SimplifiesSelectiveCoordination

Better Value

SmallerFootprint

Add iti ona lMain Options

Patented FuseRejection,Interlock andIndication


16/17

Quik-Spec Power Module

Fused Elevator

Shunt-Trip Disconnect

Easy to Specify andInstall

UL98 Listed Assembly

Simplifies SelectiveCoordination

Simplifies CodeCompliance

PMP Available formultiple elevatorinstallations

Power

ModuleSwitch

Power

Module

Panel

High IR Protective Devices

Compact Circuit Protector

200kA SCCR

60A 600V

Class J/CC fusing

Smallest fusibledisconnect

available

Finger-safe design

UL98 branch

circuit disconnect


17/17

Summary

NEC contains numerousrequirements related to fault levels

Understanding basics of faultcontribution can simplify efforts withcompliance

Higher wi thstand components maypresent fewer concerns

Fused system selective coordinationthrough 200kA achieved with ampratios

Cooper Tech Center Training

Fusible Design for Bui lding SystemsApril 28, 2009 (Cooper Bussmann)

NEC Emergency Systems, LegallyRequired and OptionalMay 29, 2009 (Mark Hilbert, NH Chief AHJ)

Electrical System MaintenanceAugust 18, 2009 (Jim White, Shermco)

Simplif ied Fault Current

Calculations

QUESTIONS ??

Presented by:

Dustin [email protected]

simplified sc calcs

Documents